JP6216533B2 - Fluorescent glass dosimeter measuring method, fluorescent glass dosimeter measuring device - Google Patents

Description

  The present invention relates to a fluorescent glass dosimeter measuring method and a fluorescent glass dosimeter measuring apparatus.

  As a method for measuring the radiation exposure dose, a fluorescent glass dosimeter measurement method is known. In the fluorescent glass dosimeter measurement method, the radiation exposure dose is measured using a phosphate glass (silver activated phosphate glass) containing silver ions. When phosphoric acid glass (hereinafter referred to as fluorescent glass dosimeter) is irradiated with ultraviolet rays for excitation (for example, 355 nm), radiophotoluminescence of orange (light having a peak wavelength at 600 nm to 700 nm) proportional to the radiation exposure dose ( It has the property of generating RPL (Radio Photo Luminescence). That is, the radiation exposure dose of the fluorescent glass dosimeter can be calculated by irradiating the fluorescent glass dosimeter with ultraviolet rays and measuring the fluorescence generated from the fluorescent glass dosimeter.

  However, the fluorescence generated by the fluorescent glass dosimeter includes fluorescence caused by pre-dose and contamination and fluorescence caused by radiation exposure. Therefore, in the conventional fluorescent glass dosimeter measurement method, it has been proposed to remove fluorescence caused by pre-dose and dirt from the fluorescence generated by the fluorescent glass dosimeter (see, for example, Patent Document 1).

  The fluorescence caused by the pre-dose includes a component that decays in about 1 μs (microseconds) and a component that continues to decay to about 1 ms (milliseconds). In addition, the fluorescence caused by dirt attenuates in about 1 μs. Furthermore, the fluorescence due to radiation exposure decays in about 40 μs. Therefore, in the above proposal, the fluorescence from the fluorescent glass dosimeter is detected after the component attenuated in about 1 μs of the fluorescence caused by pre-dose and the fluorescence caused by dirt are attenuated.

  However, the fluorescence includes fluorescence caused by predose. Therefore, in the above proposal, after the fluorescence caused by radiation exposure is attenuated, the fluorescence caused by the component that continues to decay until about 1 ms is detected from the fluorescence caused by the pre-dose. The difference between the fluorescence detected at the beginning (fluorescence due to radiation exposure + fluorescence due to pre-dose) and the fluorescence due to pre-dose calculated from the fluorescence detected later is taken as the fluorescence caused by radiation exposure, and the radiation exposure dose of the fluorescent glass dosimeter is Calculated.

  Moreover, in order to detect the fluorescence resulting from radiation exposure with high sensitivity, it has been proposed to detect the fluorescence by determining the sensitivity (measurement range) of the photomultiplier tube (see, for example, Patent Document 2). In this proposal, the sensitivity most suitable for detection is determined by gradually changing the sensitivity of the photomultiplier tube from low sensitivity to high sensitivity in accordance with the magnitude of fluorescence caused by radiation exposure.

JP 59-190681 A Japanese Patent Application Laid-Open No. 8-114674

  However, in the conventional method, the sensitivity of the photomultiplier tube is determined based on fluorescence resulting from radiation exposure. For this reason, when the fluorescence caused by pre-dose or the fluorescence caused by phosphate glass contamination is large, the sensitivity may be too high in the measurement range determined according to the magnitude of the fluorescence caused by radiation exposure. As a result, the photomultiplier tube may be damaged by an excessive current flowing through the photomultiplier tube. In addition, the measurement accuracy of fluorescence is not appropriate, and there is a possibility that an accurate radiation exposure dose cannot be measured.

  The present invention has been made to solve the above problems, and even when the fluorescence caused by pre-dose is large, the photomultiplier tube can be prevented from being damaged, and accurate fluorescence measurement is possible. An object is to provide a fluorescent glass dosimeter measuring method and a fluorescent glass dosimeter measuring apparatus.

The fluorescent glass dosimeter measurement method according to the present invention is a first method of irradiating a fluorescent glass dosimeter exposed to radiation with pulsed light for excitation using any one light source selected from a solid laser, a nitrogen gas laser, and a flash lamp . This is due to the irradiation step, the first detection step of detecting the fluorescence generated by the fluorescent glass dosimeter by the irradiation of the pulsed light, and the pre-dose detected after the lapse of the first time after the irradiation of the pulsed light A first integration step of integrating fluorescence including a fluorescence component and a fluorescence component resulting from radiation exposure by analog for a first sampling time, and at the time of exposure dose calculation according to the integration result in the first integration step and sensitivity determination step of determining the sensitivity of detecting the fluorescence, after performing the sensitivity determining step, a second illumination for irradiating the pulsed light on the fluorescent glass dosimeters The second detection step of detecting the fluorescence generated in the fluorescent glass dosimeter by the irradiation of the pulsed light in the second irradiation step, and the end of the irradiation of the pulsed light in the second irradiation step. A second integration step of integrating the fluorescence including the fluorescence component resulting from the pre-dose and the fluorescence component resulting from the radiation exposure detected after the elapse of 1 time in an analog manner for the first sampling time with the determined sensitivity; , Integrating the fluorescence including the fluorescence component caused by the pre-dose detected after the lapse of the second time from the end of the first sampling time in the second integration step by the second sampling time with the determined sensitivity. The fluorescent glass based on the difference between the third integration step, the integration result in the second integration step, and the integration result in the third integration step. And having a step of calculating the radiation dose amount meter, the.

  According to the present invention, since the sensitivity of the photomultiplier tube is determined using the fluorescence caused by the contamination of the fluorescent glass dosimeter, the fluorescence measuring means is damaged even when the fluorescence caused by the pre-dose is large. Can be suppressed.

It is a block diagram of the fluorescent glass dosimeter measuring device which concerns on embodiment. It is a wave form diagram of the electric signal corresponding to the fluorescence which a reference glass emits. It is a wave form diagram of the electric signal corresponding to the fluorescence which a fluorescent glass dosimeter emits. It is an example of the table data for determining a sensitivity. It is a flowchart which shows the operation | movement of a sensitivity determination. It is a flowchart which shows the operation | movement of a sensitivity determination. It is a flowchart which shows the operation | movement of radiation exposure dose calculation.

  Hereinafter, a fluorescent glass dosimeter measuring method and a fluorescent glass dosimeter measuring apparatus according to an embodiment will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a configuration diagram of a fluorescent glass dosimeter measuring apparatus 100 according to the embodiment. The fluorescent glass dosimeter measuring device 100 includes an optical system 200 that irradiates the fluorescent glass dosimeter G with excitation laser light and reads the excitation light of the fluorescent glass dosimeter G, and a control device 300 that controls the optical system 200. Prepare.

(Configuration of optical system 200)
The optical system 200 includes a solid-state laser 210 (light source), an ultraviolet transmission filter 220, a reference block 230, a plate holder 240, a filter system 250, and a photomultiplier tube 260 (detection means).

A solid-state laser 210 (Diode-Pump Solid-State Laser) irradiates excitation ultraviolet rays L (for example, a central wavelength of 355 nm) in a pulsed manner. Instead of the solid-state laser 210, an ultraviolet (e.g., a center wavelength 355 nm) nitrogen gas laser for irradiating may be using flash lamp. The ultraviolet light transmission filter 220 transmits the ultraviolet light L from the solid-state laser 210 and shields light of other wavelengths.

  The reference block 230 includes an aperture plate 231, a half mirror 232, an ultraviolet transmission filter 233, a reference glass 234, an ultraviolet cut filter 235, a photodiode 236, and a housing 237. The aperture plate 231 is formed with a slit-shaped aperture 231a for allowing the ultraviolet light L from the solid-state laser 210 to pass therethrough.

  The half mirror 232 transmits part of the ultraviolet light L that has passed through the opening 231a and reflects part of it. For this reason, the ultraviolet ray L is separated into ultraviolet rays L1 and L2 by the half mirror 232. The ultraviolet transmission filter 233 transmits the ultraviolet light L1 separated by the half mirror 232 and shields light of other wavelengths.

  The reference glass 234 is a standard fluorescent glass exposed to a predetermined amount of radiation. When the reference glass 234 is irradiated with the ultraviolet ray L1, fluorescence proportional to the intensity of the ultraviolet ray L1 and the radiation exposure dose is generated. The fluorescence generated in the reference glass 234 is used for correcting the output fluctuation of the solid-state laser 210.

  The reference glass 234 increases the radiation exposure dose over time due to natural exposure, but the reference glass 234 is exposed to a sufficient amount of radiation in advance, and the amount of fluorescence caused by the radiation becomes very large. . For this reason, the increase in the amount of fluorescence due to natural exposure can be almost ignored. Further, the fluorescence caused by pre-dose and dirt can be almost ignored.

  The ultraviolet cut filter 235 transmits the fluorescence generated in the reference glass 234 and shields the ultraviolet ray L1.

  The photodiode 236 receives the fluorescence from the reference glass 234 that has passed through the ultraviolet cut filter 235. The photodiode 236 converts the received light into an electrical signal (current signal) and outputs it. The magnitude of the electronic signal (current signal) output from the photodiode 236 is proportional to the intensity of the received fluorescence.

  The housing 237 accommodates the aperture plate 231, the half mirror 232, the ultraviolet transmission filter 233, the reference glass 234, the ultraviolet cut filter 235, and the photodiode 236.

  The plate holder 240 holds a fluorescent glass dosimeter G which is a measurement target of radiation exposure dose. When the fluorescent glass dosimeter G is irradiated with the ultraviolet light L2 separated by the half mirror 232, fluorescence proportional to the intensity of the ultraviolet light L2 and the radiation exposure dose is generated. The fluorescence includes fluorescence caused by pre-dose and dirt in addition to the fluorescence caused by radiation exposure.

  The filter system 250 includes a diaphragm 251, an ultraviolet cut filter 252, a condenser lens 253, and a band pass filter 254. The diaphragm 251 is formed with a slit-shaped opening 251a for allowing the ultraviolet light L2 separated by the half mirror 232 to pass therethrough. The ultraviolet cut filter 252 shields the ultraviolet light L2 and transmits the fluorescence generated by the fluorescent glass dosimeter G.

  The condensing lens 253 condenses the fluorescence that has passed through the ultraviolet cut filter 252. The condensed fluorescence enters the bandpass filter 254. The band pass filter 254 mainly transmits the fluorescence having a wavelength of 615 nm to 715 nm among the incident fluorescence.

  The photomultiplier tube 260 detects the fluorescence transmitted through the bandpass filter 254. The photomultiplier tube 260 converts the detected light into an electrical signal (current signal) and outputs it. The photomultiplier tube 260 mainly detects fluorescence having a wavelength of 300 nm to 900 nm. The magnitude of the electronic signal (current signal) output from the photomultiplier tube 260 is proportional to the detected fluorescence intensity.

  The photomultiplier tube 260 is configured to change the sensitivity (measurement range) by changing the applied voltage. Specifically, the sensitivity increases when the applied voltage to the photomultiplier tube 260 is increased, and the sensitivity decreases when the applied voltage to the photomultiplier tube 260 is decreased.

(Configuration of control device 300)
The control device 300 includes a drive circuit 310, a preamplifier 320, a preamplifier 330, a timing circuit 340, an integration circuit 350 (integration means), an AD converter 360, and a control circuit 370 (sensitivity determination means, sensitivity setting means, exposure). Dose calculating means).

  The drive circuit 310 controls the irradiation of the solid-state laser 210 with ultraviolet rays based on an instruction from the control circuit 370. Specifically, the drive circuit 310 controls the solid-state laser 210 so as to irradiate ultraviolet rays in a pulse shape (for example, several ns (nanoseconds)). The solid-state laser 210 emits light for several ns when a trigger signal is input.

  The preamplifier 320 converts the electrical signal (current signal) output from the photodiode 236 into a voltage signal. The electrical signal converted into a voltage by the preamplifier 320 is input to the subsequent timing circuit 340 and the integrating circuit 350. The preamplifier 330 converts an electrical signal (current signal) output from the photomultiplier tube 260 into a voltage signal. The electrical signal converted into a voltage by the preamplifier 330 is input to the integrating circuit 350 at the subsequent stage.

  The timing circuit 340 generates and outputs a trigger signal serving as a signal for starting integration to the integration circuit 350. Using the logical product (AND) of the input from the preamplifier 320 and the input from the control circuit 370 as a trigger (cue), a trigger signal indicating the timing of integration disclosure in the integration circuit 350 is output.

  The integration circuit 350 integrates the voltage signals output from the preamplifier 320 and the preamplifier 330 when the trigger signal from the timing circuit 340 is input.

(Integration of voltage signal output from preamplifier 320)
FIG. 2 is a waveform diagram of a voltage signal input from the preamplifier 320 to the integration circuit 350. As already described, the reference glass 234 is exposed to radiation to such an extent that fluorescence caused by pre-dose and contamination can be relatively ignored.

  For this reason, as shown in FIG. 2, the fluorescence caused by pre-dose and contamination hardly appears in the waveform of the voltage signal input from the preamplifier 320 to the integration circuit 350. The timing circuit 340 outputs a trigger signal at time T1 when signals are input from the preamplifier 320 and the control circuit 370 (in practice, a trigger signal is also output at time T3 described later, (The explanation is omitted.) The integration circuit 350 starts integration of the voltage signal when the trigger signal is input, and ends the integration at time T2.

  That is, the integrating circuit 350 integrates the electric signal between T1 and T2 shown in FIG. This is equivalent to obtaining the area of the hatched portion shown in FIG. 2 (hereinafter referred to as REF). The integration circuit 350 outputs the calculated REF. The values of T1 and T2 are determined by the glass composition of the fluorescent glass dosimeter G. Further, the REF output from the integration circuit 350 is used for correcting the output fluctuation of the solid-state laser 210.

(Integration of voltage signal output from preamplifier 330)
FIG. 3 is a waveform diagram of a voltage signal input from the preamplifier 330 to the integration circuit 350. The timing circuit 340 outputs a trigger signal at times T1 and T3 when signals are input from the preamplifier 320 and the control circuit 370. When the trigger signal is input, the integration circuit 350 integrates the voltage signal input from the preamplifier 330 for a predetermined time. Specifically, the integration circuit 350 starts the integration of the voltage signal at time T1, and ends the integration at time T2. Further, the integration circuit 350 starts integration of the voltage signal at time T3 and ends integration at time T4.

  That is, the integrating circuit 350 integrates the electric signals between T1 and T2 and between T3 and T4 shown in FIG. This is equivalent to obtaining the areas of the hatched portions from T1 to T2 (hereinafter referred to as RPL) and the hatched portions from T3 to T4 (hereinafter referred to as LD) shown in FIG. The integration circuit 350 outputs the calculated RPL and LD. The values of T3 and T4 are determined by the glass composition of the fluorescent glass dosimeter G.

  The AD converter 360 converts the REF, RPL, and LD output from the integration circuit 350 from an analog signal to a digital signal and outputs the converted signal.

  The control circuit 370 is, for example, a microcomputer. The control circuit 370 controls the drive circuit 310 and the timing circuit 340. Specifically, the control circuit 370 instructs the drive circuit 310 to irradiate ultraviolet rays from the solid state laser 210. In addition, the control circuit 370 instructs the timing circuit 340 to output a trigger signal. The control circuit 370 stores the digitized values of REF, RPL, and LD output from the AD converter 360. Further, the control circuit 370 determines the sensitivity of the photomultiplier tube 260 and calculates the radiation exposure dose.

(Determination of sensitivity)
Here, determination of sensitivity by the control circuit 370 will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of table data stored in the control circuit 370. As shown in FIG. 4, the control circuit 370 has sensitivity (measurement range), a range R1 (R1 = RPL / REF) obtained by dividing RPL by REF (where n2 <n1), and applied voltage (V). It is stored in association. When REF, RPL, and LD are output from the AD converter, the control circuit 370 calculates a value R1 obtained by dividing RPL by REF.

  The control circuit 370 determines in which range of the table data shown in FIG. 4 the calculated value of R1 is included, and determines the sensitivity of the photomultiplier tube 260. The control circuit 370 measures at the lowest sensitivity (level 7). If the sensitivity is too low at level 7, the sensitivity is increased and further measurement is performed. In FIG. 4, the range of sensitivity (measurement range) is five, but the range of sensitivity (measurement range) may be further subdivided.

(Calculation of radiation exposure dose)
Next, calculation of the radiation exposure dose by the control circuit 370 will be described with reference to FIGS. As described above, out of the REF, RPL, and LD output from the AD converter, the RPL includes the fluorescence component (LD ′) of the component that continues to be attenuated to about 1 ms (milliseconds) of the fluorescence caused by the pre-dose. And a fluorescent component (denoted as SAMP) resulting from radiation exposure. For this reason, in order to obtain SAMP, it is necessary to remove the fluorescent component (LD ′) resulting from pre-dose from RPL.

Here, the fluorescence component LD ′ caused by the pre-dose in the RPL shown in FIG. 3 can be expressed by the following equation (1).
LD ′ = fps × LD (1)
Note that fps is a constant unique to the fluorescent glass dosimeter measuring apparatus 100.

Moreover, the fluorescence component SAMP resulting from radiation exposure in RPL can be expressed by the following (2) using the above equation (1).
SAMP = RPL-fps × LD (2)

  The control circuit 370 calculates the SAMP by subtracting the fluorescence component (LD ′) caused by the pre-dose from the RPL using the above-described equations (1) and (2). Next, the control circuit 370 calculates a value R2 obtained by dividing the calculated SAMP by REF, and multiplies the predetermined coefficient (constant) to calculate the radiation exposure dose of the fluorescent glass dosimeter G.

(Operation of fluorescent glass dosimeter measuring apparatus 100)
5A to 5B are flowcharts showing the sensitivity determination operation of the fluorescent glass dosimeter measuring apparatus 100. FIG. FIG. 6 is a flowchart showing the radiation exposure dose calculation operation of the fluorescent glass dosimeter measuring apparatus 100. Hereinafter, the operation of the fluorescent glass dosimeter measuring apparatus 100 will be described with reference to FIGS. 5A to 5B and 6.

(Sensitivity setting operation)
First, the sensitivity setting operation will be described with reference to FIG.
The control circuit 370 controls the voltage applied to the photomultiplier tube 260 to set the photomultiplier tube 260 to the lowest sensitivity (level 7) (step S101). Specifically, the control circuit 370 sets the applied voltage of the photomultiplier tube 260 to V1.

  The control circuit 370 controls the drive circuit 310 to irradiate the solid-state laser 210 with the ultraviolet rays L in a pulse shape (step S102).

  The ultraviolet light L passes through the ultraviolet transmission filter 220 and enters the aperture plate 231 of the reference block 230. The ultraviolet light L is slit-shaped by the opening 231 a of the opening plate 231 and enters the half mirror 232. The half mirror 232 separates the incident ultraviolet light L into ultraviolet light L1 introduced into the reference glass 234 and ultraviolet light L2 introduced into the fluorescent glass dosimeter G (step S103).

  The ultraviolet light L1 passes through the ultraviolet transmission filter 233 and then enters the reference glass 234 (step S104). When the ultraviolet ray L1 is incident, the reference glass 234 generates fluorescence corresponding to the intensity of the ultraviolet ray L1 and the radiation exposure dose (step S105).

  The fluorescence generated in the reference glass 234 passes through the ultraviolet cut filter 235 and enters the photodiode 236. When the fluorescence is incident, the photodiode 236 converts the fluorescence into a current signal proportional to the intensity (step S106).

  The ultraviolet ray L <b> 2 has a slit shape due to the opening 251 a of the diaphragm 251. The slit-shaped ultraviolet ray L2 enters the fluorescent glass dosimeter G accommodated in the plate holder 240 (step S107).

  When the ultraviolet ray L2 is incident, the fluorescent glass dosimeter G generates fluorescence corresponding to the intensity of the ultraviolet ray L2 and the radiation exposure dose (step S108).

  Fluorescence generated by the fluorescent glass dosimeter G passes through the ultraviolet cut filter 252 and enters the condenser lens 253. The fluorescence is collected by the condenser lens 253 and incident on the band pass filter 254 and then incident on the photomultiplier tube 260. The photomultiplier tube 260 detects the fluorescence transmitted through the bandpass filter 254, converts the detected fluorescence into a current signal, and outputs the current signal (step S109).

  The preamplifiers 320 and 330 respectively convert the current signals output from the photodiode 236 and the photomultiplier tube 260 into voltage signals (step S110).

  Further, the timing circuit 340 outputs a trigger signal in accordance with an instruction from the control circuit 370 (step S111).

  When the trigger signal is input from the timing circuit 340, the integration circuit 350 integrates the voltage signals output from the preamplifier 320 and the preamplifier 330, and calculates REF, RPL, and LD described with reference to FIGS. (Step S112). The integration circuit 350 outputs the calculated REF, RPL, and LD. In the determination of sensitivity, the value of LD is not necessary. For this reason, in step S112, only REF and RPL may be calculated.

  The AD converter 360 converts the REF, RPL, and LD output from the integration circuit 350 from an analog signal to a digital signal and outputs the converted signal (step S113).

  The control circuit 370 calculates a value R1 (R1 = RPL / REF) obtained by dividing RPL converted into a digital signal by REF (step S114). By dividing RPL by REF, output fluctuation of the solid-state laser 210 can be corrected.

  Next, the control circuit 370 determines to which of the ranges shown in FIG. 4 the value R1 = RPL / REF obtained by dividing RPL by REF belongs, and sets the sensitivity of the photomultiplier tube 260 (step S1115). The operation in step S115 will be described in detail with reference to FIG. 5B.

  FIG. 5B is a flowchart showing the operation of step S115 of FIG. 5A. Hereinafter, the sensitivity setting of the photomultiplier tube 260 will be described in detail with reference to FIGS. 4 and 5B.

  The control circuit 370 determines whether the value R1 = RPL / REF obtained by dividing RPL by REF is within the range of level 7 shown in FIG. 4 (n1 ≦ R1) (step S201). When R1 is within the range of level 7 (n1 ≦ R1) (Yes in step S201), the control circuit 370 completes the setting operation. This is because the sensitivity of the photomultiplier tube 260 has already been set to level 7.

  When the value of R1 is not within the range of level 7 (n1 ≦ R1) (No in step S201), the control circuit 370 determines whether R1 is within the range of level 6 (n2 ≦ R1 <n1) (step S202). ). When R1 is within the range of level 6 (n2 ≦ R1 <n1) (Yes in step S202), the control circuit 370 sets the sensitivity of the photomultiplier tube 260 to level 6 (step S203).

  When the value of R1 is not within the range of level 6 (n2 ≦ R1 <n1) (No in step S202), the control circuit 370 sets the sensitivity of the photomultiplier tube 260 to level 5 (step S204). Specifically, the control circuit 370 sets the voltage applied to the photomultiplier tube 260 to V3.

  Here, the photomultiplier tube 260 is set to level 5. If the photomultiplier tube 260 remains set to level 7, the sensitivity of the photomultiplier tube 260 is too low, and the RPL of the measurement target is set. This is because it cannot be determined whether the value falls between level 5 and level 3.

  Next, with the sensitivity of the photomultiplier tube 260 set to level 5, the control circuit 370 controls the drive circuit 310, the timing circuit 340, etc., and performs the operations of steps S102 to S114 in FIG. 5A ( Step S205).

  Next, the control circuit 370 determines whether R1 is within the level 5 range (n1 ≦ R1) (step S206). When R1 is within the range of level 5 (n1 ≦ R1) (Yes in step S206), the control circuit 370 completes the setting operation. This is because the sensitivity of the photomultiplier tube 260 has already been set to level 5.

  When the value of R1 is not within the range of level 5 (n1 ≦ R1) (No in step S206), the control circuit 370 determines whether R1 is within the range of level 4 (n2 ≦ R1 <n1) (step S207). ). When R1 is within the range of level 4 (n2 ≦ R1 <n1) (Yes in step S207), the control circuit 370 sets the sensitivity of the photomultiplier tube 260 to level 4 (step S208).

  When the value of R1 is not within the range of level 4 (n2 ≦ R1 <n1) (No in step S207), the control circuit 370 sets the sensitivity of the photomultiplier tube 260 to level 3 (step S209).

  In the operation described with reference to FIG. 5B, fluorescence (RPL) is measured at level 7 and level 5 in order to shorten the time required for sensitivity setting. You may make it set a sensitivity by measuring.

  Specifically, when R1 is not within the range of level 7, the sensitivity of the photomultiplier tube 260 is set to level 6 and fluorescence (RPL) is measured. When R1 is not within the range of level 7, the sensitivity of the photomultiplier tube 260 is set to level 6 and fluorescence (RPL) is measured to determine whether R1 is within the range of level 6.

  If R1 is not in the level 6 range, the sensitivity of the photomultiplier tube 260 is set to level 5 and fluorescence (RPL) is measured to determine whether R1 is in the level 5 range. In this way, the sensitivity (level) of the photomultiplier tube 260 may be increased one by one to measure fluorescence (RPL), and the sensitivity of the photomultiplier tube 260 may be set.

(Operation of radiation exposure dose calculation)
Next, the radiation exposure dose calculation operation will be described with reference to FIG.
The control circuit 370 controls the drive circuit 310 to irradiate the pulsed ultraviolet light L from the solid-state laser 210 (step S301).

  The ultraviolet light L passes through the ultraviolet transmission filter 220 and enters the aperture plate 231 of the reference block 230. The ultraviolet light L is slit-shaped by the opening 231 a of the opening plate 231 and enters the half mirror 232. The half mirror 232 separates the incident ultraviolet light L into ultraviolet light L1 introduced into the reference glass 234 and ultraviolet light L2 introduced into the fluorescent glass dosimeter G (step S302).

  The ultraviolet ray L1 passes through the ultraviolet ray transmission filter 233 and then enters the reference glass 234 (step S303). When the ultraviolet ray L1 is incident, the reference glass 234 generates fluorescence corresponding to the intensity of the ultraviolet ray L1 and the radiation exposure dose (step S304).

  The fluorescence generated in the reference glass 234 passes through the ultraviolet cut filter 235 and enters the photodiode 236. When the fluorescence is incident, the photodiode 236 converts the fluorescence into a current signal proportional to the intensity (step S305).

  The ultraviolet ray L <b> 2 has a slit shape due to the opening 251 a of the diaphragm 251. The slit-shaped ultraviolet ray L2 enters the fluorescent glass dosimeter G accommodated in the plate holder 240 (step S306). The fluorescent glass dosimeter G is not necessarily accommodated in the plate holder 240.

  When the ultraviolet ray L2 is incident, the fluorescent glass dosimeter G generates fluorescence corresponding to the intensity of the ultraviolet ray L2 and the radiation exposure dose (step S307).

  Fluorescence generated by the fluorescent glass dosimeter G passes through the ultraviolet cut filter 252 and enters the condenser lens 253. The fluorescence is collected by the condenser lens 253 and incident on the band pass filter 254 and then incident on the photomultiplier tube 260. The photomultiplier tube 260 detects the fluorescence transmitted through the band-pass filter 254, converts the detected fluorescence into a current signal, and outputs it (step S308).

  The preamplifiers 320 and 330 respectively convert the current signals output from the photodiode 236 and the photomultiplier tube 260 into voltage signals (step S309).

  Further, the timing circuit 340 outputs a trigger signal according to an instruction from the control circuit 370 (step S310).

  When the trigger signal is input from the timing circuit 340, the integration circuit 350 integrates the voltage signals output from the preamplifier 320 and the preamplifier 330, and calculates REF, RPL, and LD described with reference to FIGS. (Step S311). The integration circuit 350 outputs the calculated REF, RPL, and LD.

  The AD converter 360 converts the REF, RPL, and LD output from the integration circuit 350 from an analog signal to a digital signal and outputs the converted signal (step S312).

  The control circuit 370 calculates LD ′ from LD using the above-described equation (1), and then calculates SAMP obtained by subtracting the fluorescence component (LD ′) caused by predose from RPL using the equation (2). (Step S313). Next, the control circuit 370 calculates a value R2 obtained by dividing the calculated SAMP by REF (step S314). By dividing by REF, the output fluctuation of the solid-state laser 210 is corrected.

  Next, the control circuit 370 multiplies the calculated value R2 by a predetermined coefficient (constant) to calculate the radiation exposure dose of the fluorescent glass dosimeter G (step S315).

  As in the case of determining the sensitivity of the photomultiplier tube 260, the fluorescent glass dosimeter is irradiated with ultraviolet rays from the solid-state laser 210 a plurality of times in a pulsed manner and using the average value of SAMP / REF calculated for each irradiation. The radiation exposure dose of G may be calculated.

  As described above, in the present invention, the sensitivity of the photomultiplier tube is determined using RPL including fluorescence (LD ') caused by pre-dose and fluorescence (SAMP) caused by radiation exposure. For this reason, even when the fluorescence resulting from pre-dose is high, it is possible to suppress an excessive current from flowing through the photomultiplier tube 260. As a result, it is possible to reduce the possibility of damage to the photomultiplier tube 260 and to accurately measure the amount of fluorescence.

  Usually, the fluorescence LD ′ caused by pre-dose is subtracted from the RPL in FIG. 3, and the sensitivity of the photomultiplier tube is determined using fluorescence (SAMP) caused by radiation exposure. However, when only the fluorescence (SAMP) due to radiation exposure is used, the sensitivity may be too high when the fluorescence due to pre-dose is large. As a result, the photomultiplier tube may be damaged by an excessive current flowing through the photomultiplier tube. The present invention can reduce such problems.

  The present invention can suppress an excessive current from flowing even when fluorescence caused by pre-dose is high. For this reason, it is suitable for the fluorescent glass dosimeter measuring method and measuring apparatus using an expensive photomultiplier tube.

  DESCRIPTION OF SYMBOLS 100 ... Fluorescent glass dosimeter measuring device, 200 ... Optical system, 210 ... Solid laser (light source), 220 ... Ultraviolet transmission filter, 230 ... Reference block, 231 ... Opening plate, 231a ... Opening, 232 ... Half mirror, 233 ... Ultraviolet Transmission filter, 234 ... reference glass, 235 ... UV cut filter, 236 ... photodiode, 237 ... housing, 240 ... plate holder, 250 ... filter system, 251 ... diaphragm, 251a ... opening, 252 ... UV cut filter, 253 ... Condenser lens, 254... Band pass filter, 260... Photomultiplier tube (detection means), 300... Control device, 310... Drive circuit, 320, 330 ... preamplifier, 340 ... timing circuit, 350. 360 ... Converter 370 ... Control circuit Sensitivity decision unit, the sensitivity setting unit, the exposure dose calculation means), G ... fluorescent glass dosimeters, L, L1, L2 ... UV.

Claims (4)

A first irradiation step of irradiating a fluorescent glass dosimeter exposed to radiation with pulsed light for excitation using any one light source selected from a solid-state laser, a nitrogen gas laser, and a flash lamp ;
A first detection step of detecting fluorescence generated by the fluorescent glass dosimeter by irradiation with the pulsed light;
A first integration in which fluorescence including a fluorescence component resulting from pre-dose and a fluorescence component resulting from radiation exposure detected after a lapse of a first time from the end of irradiation of the pulsed light is analog- accumulated for a first sampling time. Process,
A sensitivity determination step for determining the sensitivity for detecting the fluorescence at the time of calculating the exposure dose according to the integration result in the first integration step ;
A second irradiation step of irradiating the fluorescent glass dosimeter with the pulsed light after performing the sensitivity determination step;
A second detection step of detecting fluorescence generated by the fluorescent glass dosimeter by irradiation of the pulsed light in the second irradiation step;
Fluorescence including a fluorescence component resulting from pre-dose and a fluorescence component resulting from radiation exposure detected after a lapse of a first time from the end of irradiation of the pulsed light in the second irradiation step is measured with the determined sensitivity. A second integration step of integrating by analog for one sampling time;
The fluorescence including the fluorescence component caused by the pre-dose detected after the elapse of the second time from the end of the first sampling time in the second integration step is integrated in the analog for the second sampling time with the determined sensitivity. A third integrating step;
A step of calculating a radiation exposure dose of the fluorescent glass dosimeter based on a difference between an integration result in the second integration step and an integration result in the third integration step;
A method for measuring a fluorescent glass dosimeter, comprising: Prior Symbol sensitivity determination step, when the integration result of the first integration step is greater than a threshold, the sensitivity is lowered, when the integration result of the first integration step is less than the threshold value, to increase the sensitivity The fluorescent glass dosimeter measuring method according to claim 1. Any one light source selected from a solid-state laser, a nitrogen gas laser, and a flash lamp for irradiating a fluorescent glass dosimeter exposed to radiation with a pulsed light for excitation;
Detection means for detecting fluorescence generated by the fluorescent glass dosimeter by irradiation of the pulsed light;
The fluorescence including the fluorescence component caused by the pre-dose detected by the detection means and the fluorescence component caused by radiation exposure after the first time has elapsed since the end of the irradiation of the pulsed light is integrated by analog for the first sampling time. Integrating means for obtaining a first integration result ;
Sensitivity determining means for determining the sensitivity for detecting fluorescence at the time of calculating the exposure dose according to the first integration result;
Exposure dose calculating means for calculating the radiation exposure dose of the fluorescent glass dosimeter;
With
The integration means, in situations where the sensitivity is determined by the sensitivity decision unit, the fluorescent component and radiation exposure due to Puredozu detected in the previous SL detecting means from the end of irradiation of the pulsed light after the first time Fluorescence including the resulting fluorescence component is integrated by analog for the first sampling time with the determined sensitivity to obtain a second integration result, and a second time has elapsed since the end of the first sampling time. after the fluorescence comprising a fluorescent component due to the detected Puredozu before Symbol detection means obtains a third accumulation result by accumulating the second sampling time period analog at the determined sensitivity,
The exposure dose calculation means calculates a radiation exposure dose of the fluorescent glass dosimeter based on a difference between the second integration result and the third integration result.
A fluorescent glass dosimeter measuring device characterized by that. The sensitivity determination means reduces the sensitivity when the first integration result is greater than a threshold value, and increases the sensitivity when the first integration result is less than or equal to the threshold value. 3. The fluorescent glass dosimeter measuring device according to 3.

Images